1. Field of the Invention
The present invention relates to a light emitting diode element, the light emission efficiency of which is improved by emitting the light from a light emitting layer externally thereof without any loss.
2. Description of the Related Art
As one example of light emitting diode element (hereinafter abbreviated as xe2x80x9cLED elementxe2x80x9d) nitride compound based blue color LED element 10 having a light emitting layer made of GaN, InGaN has been known. FIG. 1 is a front view, partly in longitudinal cross section, showing the structure of the LED element 10 of this type. A reference numeral denotes a sapphire substrate, on which a low temperature buffer layer 2 made of GaN is formed. An n-type layer 3 is formed on the GaN buffer layer 2. The n-type layer 3 is of the laminate layer structure of GaN compound semiconductor including, for example, n-type GaN current diffusion layer and AlGaN clad layer. The low temperature buffer layer 2 made of GaN serves to improve the crystal quality of the semiconductor of the n-type layer 3 formed thereon.
An active layer 4 which is formed of, for example InGaN based compound semiconductor constitutes a light emitting layer. A p-type layer 5 is formed on the active layer 4. The p-type layer 5 is of the laminate structure of GaN based compound semiconductor including for example, p-type GaN current diffusion layer and an AlGaN clad layer. In such a manner, the GaN based compound semiconductor layer including the n-type layer 3, the active layer 4 serving as a light emitting layer and the p-type layer is laminated on the sapphire substrate.
A current diffusion film of an appropriate electrically conductive material is formed on the p-type layer 5 in a planar manner for supplying a uniform current to the light emitting layer. An n side electrode 7 is formed on the surface of the n-type layer 3. A p side electrode 8 is formed on the surface of the current diffusion film 6. An LED element 10 of this type is mounted on a circuit board on the side of the sapphire substrate 1 so that output light is emitted from the light emitting layer on the side of the current diffusion film 6. A given wiring pattern is formed on the circuit substrate. Conduction of a current through the n and p side electrodes 7 and 8 of the LED element 10 causes the output light E to be emitted from the LED element 10 via the current diffusion film 6.
In such a manner, conventional LED element 10 is mounted on the circuit board on the sapphire substrate 1 on which a given wiring pattern is formed so that output light is emitted from the current diffusion film 6. However, the light transmission factor of the current diffusion film 6 which is formed of an appropriate electrically conductive material is in the order of 50 to 60% at most. 40 to 50% of the emitted light is lost when the output light emitted from the light emitting layer is transmitted through the current diffusion film 6. Therefore, there is a problem in that the light emission efficiency of the LED element 10 is lowered.
The present invention is made in view of the above-mentioned problem.
It is an object of the present invention to provide an LED element having an improved light emission efficiency by externally emitting the output light from the light emitting layer without any loss.
The above-mentioned object of the present invention is accomplished by providing a light emitting diode element having a sapphire substrate, a GaN based compound semiconductor film forming a light emitting layer which is laminated on said substrate and a current diffusion film which is formed on the semiconductor layer, in which said current diffusion film is formed of an electrically conductive metal film having a high reflectance factor for light and said light emitting diode element is mounted on a circuit board so that output light of the light emitting layers emitted from the sapphire substrate side together with light reflected on the current diffusion film.
In an aspect of the present invention, a light emitting diode element is mounted on a circuit board so that output light of a light emitting layer is reflected on a current diffusion film and then emitted from the sapphire substrate side. Therefore, the current diffusion film which otherwise lowers the light emission efficiency to the light emitting layer is utilized as means for enhancing the output light. The light emission efficiency of the light emitted diode is remarkably improved.